1. Field of the Invention
The present invention relates to an optical switch device for use in optical communication.
2. Description of the Related Art
In an optical communication network, wavelength multiplexing is performed whereby transmission capacity can be increased in a single optical transmission line. It should be noted that an optical signal of the same wavelength cannot be multiplexed in the same optical transmission line. Thus, when the multiplexing of optical signals of the same wavelength is desired, each node is required to convert the wavelength by a wavelength switch. Each node is also required to flexibly change the capacity in response to demand between any two nodes. Therefore, each node needs to function as a space switch. As described above, the fact that an optical communication network node needs a space switch function and a wavelength switch function is disclosed in, for example, a cited reference (T. Shiragaki et al., entitled "Optical Cross-connect System using Fixed-Wavelength Converters to Avoid Wavelength Blocking", First Optoelectronics and Communications Conference (OECC '96), Technical Digest, PD1-5, pp. 10-11, 1996).
Heretofore, a method of realizing both of the space switch function and the wavelength switch function has needed to provide a space switch section and a wavelength switch section independently of each other. FIG. 1 is a block diagram of a prior-art optical switch device.
FIG. 1 shows an example of a 3-input/3-output type (hereinafter referred to as 3.times.3 gate type) optical switch device. Space switch section 607 and wavelength switch section 608 are disposed independently of each other.
In space switch section 607, semiconductor optical amplifiers are used for optical gate switches. When a current flows through a semiconductor optical amplifier, the amplifier has a gain. When the current does not flow, the amplifier does not have a gain and input light is thus absorbed. A gate switch operation, that is, an on/off operation can be therefore performed by the semiconductor optical amplifier. This characteristic of a semiconductor optical amplifier gate switch (hereinafter referred to as SOAG) 604 is used, in which the space switch is constituted as described below. The optical signal to be inputted to input terminal 601 is divided into three by optical divider 603. The divided signals are connected to three SOAGs 604. Output terminals of the three SOAGs 604 connected to the same optical divider are connected to three different opticalcouplers 605 (cross connection) as shown in FIG. 1. Outputs of opticalcouplers 605 are connected to the output terminals. SOAG 604 is turned on/off, whereby a single optional optical signal alone can be inputted to one opticalcoupler 605. Since SOAGs 604 intervene in routes composed of all combinations of the connections between input terminals 601 and output terminals 602, all the combinations of switching statuses can be generated. Space switch section 607 functions as the 3.times.3 gate type space switch. The SOAG and the space switch using the SOAG are described in, for example, the cited reference (S. Takahashi et al., entitled "10 Fb/s/ch Space-Division Optical Cell Switching with 8.times.8 Gate Type Switch Matrix Employing Gate Turn-on-Delay Compensator", 1996 International Topical Meeting on PHOTONICS IN SWITCHING Technical Digest Vol. 2, PThC 1, pp. 12-15, 1996).
For a wavelength multiplexing transmission, the optical signal to be multiplexed must have different wavelengths in a single optical fiber. In order that the optical signal outputted from space switch section 607 is transmitted by multiplexing the wavelength thereof, a wavelength conversion is therefore necessary in such a manner that the same wavelength is not multiplexed. Therefore, in FIG. 1, the output of space switch section 607 is inputted to wavelength switch section 608, whereby the wavelength conversion is required. Wavelength converter 606 can be constituted by using a four-wave mixing (for example, see the cited reference: J. Zhou et al., entitled "Four-Wave Mixing Wavelength Conversion Efficiency in Semiconductor Traveling-Wave Amplifiers Measured to 65 nm of Wavelength Shift", IEEE Photon Technol. Lett., vol. 6, no. 8, pp. 984-987, 1994); a cross-gain modulation (for example, see the cited reference: D. D. Marcenac, et al., entitled "Bandwidth enhancement of wavelength conversion via cross-gain modulation by semiconductor optical amplifier cascade", Electron Lett., vol. 31, no. 17, pp. 1442-1443, 1995); a cross-phase modulation (for example, see the cited reference: B. Mikkelsen et al., entitled "All-optical noise reduction capability of Interferometric wavelength converters", Electron Lett., vol. 32, no. 6, pp. 566-567, 1996) or the like. An output light from output terminal 602 of wavelength switch section 608 is inputted to a wavelength multiplexer (not shown) and the wavelength is multiplexed, whereby the wavelength-multiplexed optical signal can be transmitted to other node.
As described above, the optical switch device constituted as shown in FIG. 1 is used, whereby each node can obtain a wavelength conversion function and a switch function. However, in this constitution, the space switch section and the wavelength switch section must be prepared independently of each other. A packaging volume of the optical switch device is thus increased. Disadvantageously, this increases a cost.